This invention relates to cross-fire tubes utilized to connect adjacent combustors in a combustion apparatus, and more specifically, to cross-fire tubes which are to be secured between adjacent combustor liner collars in industrial gas turbines to insure substantially simultaneous ignition in all of the combustors.
Various constructions for cross-fire tubes are known in the field of combustion engineering. Examples of such constructions disclosed in the patent literature may be seen in U.S. Pat. Nos. 2,437,385; 2,729,938; 3,344,601 and 3,991,560.
Currently utilized cross-fire tubes exhibit undesirable wear at the interfaces between the tube and adjacent combustion liner collars due to vibration levels in the liners from combustion dynamic pressure fluctuations. In addition, heavy wear has been exhibited in the current cross-fire tube retainers and between the retainers and the combustion casings, combustion covers and/or combustion flow sleeves. As a result, cross-fire tubes and/or retainers must be replaced at relatively frequent intervals.
In response to such problems, solutions have been proposed based on a careful selection of materials and modifications of the methods of attachment of the cross-fire tube retainers. This methodology has resulted only in increasing parts life limited to current inspection intervals, so that both the cross-fire tubes and associated retainers continue to be considered consumable spares.
It is therefore the principal object of this invention to provide a new improved cross-fire tube construction having a longer service life and yielding longer service intervals by minimizing or eliminating friction wear at all liner collar/cross-fire tube interfaces. This is accomplished in the present invention by providing a cross-fire tube having a main body and end connectors which are flexible and spring loaded in axial and radial directions, respectively. By this arrangement, a spring clamping force between the cross-fire tube and the combustion liner collar is provided which is greater than the friction forces generated due to inertial effects and vibration. In other words, the amplitude of the vibration portion of the loading is absorbed by the spring action of the cross-fire tube itself.
More specifically, and in a first exemplary embodiment of the invention, a spring loaded cross-fire tube is provided which includes a flexible main body portion which is generally tubular and substantially cylindrical in shape, provided with a series of staggered circumferential saw cuts to thereby provide a flexible and compressible spring body. At either end of the main spring body portion, there is a connector portion which includes an integral, inner sleeve which is provided with a series of circumferentially spaced, axial cuts to thereby form a plurality of annularly arrayed spring fingers which are configured so as to apply a radially outwardly directed force against an inside surface of the combustion liner collar when the connector is inserted within the latter. In this first exemplary embodiment, each connector portion of the cross-fire tube also includes an outer connector sleeve which is also provided with a plurality of circumferentially spaced axial cuts to form a second set of spring loaded fingers which are configured to apply a radially inwardly directed force against an outside surface of the liner collar. With the combustor liner collars inserted or received within, i.e., between, the first and second sets of fingers at each end of the main spring body, spring forces are thus exerted in opposite radial directions against both inside and outside surfaces of the collar to firmly secure the cross-fire tube in place between adjacent collars. In the assembled state, the main spring body is also loaded in axial compression.
It is another feature of this first exemplary embodiment that the main spring body is covered by a thin metal pressure cover or sleeve in concentric relation thereto, with contact between the sleeve and the main spring body portion occurring at opposite ends of the cover (adjacent the connectors), and at a point approximately midway between the ends of the cover where the latter is tack welded to the main spring body.
The cross-fire tube as described allows compression and expansion of the main spring body, as well as flexing action of the main body and the connector portions during operation to thereby eliminate or at least minimize friction wear caused by relative sliding movement at the cross-fire tube/liner collar interfaces.
In a second exemplary embodiment of the invention, the main spring body portion of the cross-fire tube comprises a substantially cylindrical coil spring, covered by a fabric woven from steel wires and ceramic threads.
The ends of the coil spring are secured at opposite ends to connector sleeves which are designed to be inserted within respective combustor liner collars. In this second exemplary embodiment, the connector sleeves are axially cut about their respective peripheries to form a sets of spring fingers which exert radially outwardly directed forces against inside surfaces of the collars. Unlike the first described embodiment-, no outer connector sleeves are required.
In a third exemplary embodiment of the invention, the main spring body portion of the cross-fire tube comprises a wire mesh fabric which has been shaped as a corrugated sleeve or bellows and then heat treated so as to maintain the shape at high temperatures. The bellows or corrugated shape imparts spring characteristics to the main body portion, thus permitting the cross-fire tube to expand, contract, and flex under operating conditions. The wire mesh fabric also permits transpirational cooling of the cross-fire tube to thereby prolong its service life. As in the second exemplary embodiment, the main body portion has secured at opposite ends connector sleeves which include a plurality of spring loaded fingers adapted to exert radially outwardly directed forces against the inside surfaces of the combustor liner collars.
In a fourth (and preferred) embodiment, the cross-fire tube comprises a metal, tubular bellows with connectors at each end, the connectors including annular arrangements of radially inner and outer spring fingers in circumferentially overlapping relationship. These end connectors are designed to receive the liner collars in telescoping relationship so that the cross-fire tube exerts both axial and radial outward forces on the collar. The stiffness or spring rate of the bellows is such that any vibratory movements of the liner collars are taken up by the bellows in high cycle fatigue, thereby substantially reducing wear at the tube/liner collar interfaces.
It will be appreciated that in each of the above described embodiments, the length of the cross-fire tube exceeds the distance between the liner collars to thereby insure compressive spring loading of the cross-fire tubes when assembled in place.
Thus, in its broader aspects, the present invention comprises a cross-fire tube for attachment to liner collars of adjacent combustors in a combustion apparatus comprising an elongated, axially elastically compressible and substantially cylindrical body having connecting portions at either end thereof, each connecting portion including first spring means including a plurality of circumferentially spaced spring fingers for exerting radially outwardly directed spring forces at least against inside surfaces of the liner collars.
The above described exemplary embodiments of the invention provide longer service intervals for cross-fire tubes by reason of the multiple spring loading characteristics thereof which eliminate the relative motion and wear between the cross-fire tubes and associated combustion liners. The selection of stiffness values for the main body and connector portions of the cross-fire tubes described above is carried out so that the tubes will flex or bend, or compress or expand before any relative frictional movement occurs. In combination with the proper selection of materials as disclosed herein with respect to the cross-fire tube body and associated connector portions, excellent high cycle fatigue life can be expected and, since the cross-fire tube connectors exert radially outwardly directed spring forces, no cross-fire tube retainers are required, thereby eliminating another source of wear in conventional cross-fire tubes.
Other objects and advantages of the invention will become apparent from the detailed description which follows.